A recirculating-ball drive has a ball nut centered on an axis and formed with an internal helical groove. A spindle received in this nut is rotatable about the axis relative to the nut and is formed with an external helical groove of substantially the same pitch as the groove of the nut. An annular row of like balls is provided in these grooves and in a passage formed in the spindle or nut so that once a ball has traveled helically and axially in one direction through one or more turns it can recirculate in the opposite axial direction via the passage. The advantage of such systems is that relative rotation of the spindle and nut axially displaces these two parts relative to each other, with the axial force being transmitted through the balls which roll on the respective parts. Thus the system has an advantage over a simple spindle threaded into a nut that the sliding friction is replaced by the considerably smaller rolling friction.
Such systems are described in German published patent applications Nos. 2,451,665 and 2,741,333. In these systems the structure forming the above-described recirculation passage is relatively complex. As a result these recirculating-ball drives are rather expensive to manufacture. Furthermore the complexity of the recirculation passage creates frictional losses that substantially reduce the efficiency of the drive, that is the ratio of force which is not transmitted from input to output but which is lost in the drive to force transmitted.